Acidification offers dairies an easy and affordable way to inactivate avian influenza virus H5N1 in raw waste milk

Philadelphia, May 7, 2024 — We know that pasteurization is an effective method for deactivating the highly pathogenic avian influenza (HPAI) H5N1 virus and ensuring the consumer milk supply is safe. But what about raw waste milk—including colostrum fed to preweaning calves and milk marked as unsaleable for consumers that farmers dispose of?

A new pilot study from the University of California, Davis published in the Journal of Dairy Science, demonstrates that simple acidification treatment with citric acid offers an effective, accessible, and easy-to-use alternative to pasteurization to ensure the safety of raw waste milk on farms for both the staff disposing of it and calves consuming it.

The study’s co-lead authors, Beate M. Crossley, DVM, MPVM, PhD, and Richard Pereira, DVM, PhD, working together with avian virology expert Rodrigo Gallardo, DVM, PhD, all from the University of California, Davis, explained, “We know from previous studies that H5N1 uniquely targets the dairy cow mammary gland, resulting in high viral loads in their milk. And not every farm has access to expensive pasteurization equipment.”

According to the US Department of Agriculture, less than 50% of large dairy operations use pasteurization on site for nonsaleable milk, with just 3% of medium operations and 1% of small dairies utilizing pasteurization for their waste milk.

The investigators noted, “Without pasteurization, and in the face of a high viral load from an infected animal, we wanted to explore accessible options for ensuring that farms can dispose of milk—or repurpose it for their calves—in a way that ensures it’s safe for human handling and animal consumption.”

Dr. Crossley’s and Dr. Pereira’s team first selected two alternative antiviral treatment options to test: milk acidification, which lowers the pH to between 4.0 and 4.5, and the lactoperoxidase system, which increases the concentration of naturally antibacterial properties in milk. Each method was tested using raw whole milk samples from a local dairy in California, all of which were first tested to measure milk quality parameters, including fat, protein, and lactose percentages. 

Three of the trials used low pathogenic avian influenza (LPAI H6N2) as a surrogate for HPAI H5N1, while the fourth trial used milk containing H5N1 from infected cows. Milk samples containing either virus then received either acidification treatment or lactoperoxidase system treatment before being inoculated into eggs and submitted for PCR testing, which is considered the gold standard for avian influenza analysis. 

Dr. Crossley remarked, “What we found shows that milk acidification is an effective and approachable way to completely kill the H5N1 virus in raw milk.”

After six hours of acidification treatment using citric acid, whole raw milk containing live avian influenza virus was fully deactivated in both the LPAI H6N2 virus trials and the HPAI H5N1 virus trial.

Dr. Pereira added, “Specifically, our recommendations—based on the trials—would be to acidify milk at a pH between 4.05 and 4.2, with an ideal target pH as close to 4.1 as possible.”

While the results are promising, the researchers emphasize that this is a pilot study and further research is needed to evaluate the on-farm effectiveness of milk acidification.

Dr. Crossley noted, “Our pilot study suggests that milk acidification could be a valuable tool for dairy farmers to manage the risk of H5N1 in nonsaleable milk.”

Dr. Pereira commented, “This method offers them an easier and more accessible alternative to pasteurization, particularly for smaller farms where pasteurization equipment may not be readily available.”

Emphasizing the impact of this study, the journal’s editor in chief, Paul Kononoff, PhD, clarified, “This research provides a foundation for developing practical strategies to mitigate the spread of H5N1 and provide safety for cows and people on dairy farms.”